The reaction of La(NO3)3·6H2O and [(n-Pr)3NH](NO3) or [(n-Bu)3NH](NO3) afforded two ionic co-crystal compounds, namely [(n-Pr)3NH]3[La(NO3)6] and [(n-Bu)3NH]3[La(NO3)6], respectively. Both compounds show switchable dielectric behaviors above room temperature, owing to their reversible structural phase transitions confirmed by DSC measurement and variable-temperature powder X-ray diffraction. The former compound can function as a thermosensitive dielectric material over a wide temperature range above room temperature, while the latter may act as a bistable dielectric material with a large ε′–T hysteresis loop. The synthetic approach affords an effective strategy to construct switchable dielectric phase transition materials based on large ammonium and lanthanide complex anion.